Method for data transmission in a vehicle

ABSTRACT

A method for data transmission from control devices to a display, which also makes possible retrofitting of a reversing aid system since it transmits the data via existing supply line(s) of further electrical loads.

BACKGROUND INFORMATION

Control devices which analyze the data from sensors and forward them toa display are used for reversing aids in a vehicle. Cables separate fromthe rest of the electrical system are incorporated into the vehicle fordata transmission from the control device to the display, which must beplaced at a location accessible to the driver. This means additionaloutlay in terms of cost and working time when a vehicle is manufactured.In a situation in which a reversing aid is to be retrofitted into avehicle, cable routing is again the actual problem, as known from thearticle “Pilot project” [Pilotprojekt], Gute Fahrt 10/91, pp. 50-53. Theoutlay is particularly great if a tractor vehicle having a trailer orsemitrailer is to be equipped with reversing aids. The coupling of thetrailer and its electrical connection via a special cable, e.g. ahelical cable with a waterproof connector, particularly increases theoutlay.

SUMMARY OF THE INVENTION

The method according to the present invention for data transmission,has, in contrast, the advantage of resorting to existing cable runs inthe vehicle. Especially in the case of possible retrofitting of avehicle with a reversing aid, it is much simpler to use the alreadyexisting cable runs as data lines and supply lines for the controldevices.

The simplest possibility for data transmission is via the electricalsupply line to which the control devices are also connected. It isparticularly advantageous in this context if the lines for loads suchas, for example, the reversing lights are used as the electrical supplyline. This has the advantage that the control device is supplied withvoltage only in a situation in which the vehicle is moving backward. Theswitch already present in the vehicle for reverse gear then serves toswitch the control device on and off.

Data transmission can also be accomplished via a further electricalsupply line which does not supply power to the control devicesthemselves.

In a further embodiment, the data transmission line selected is anelectrical supply line, e.g. the two-wire line, of a directionalindicator. Advantageously, the supply line for the reversing light isalso selected for data transmission via a two-wire line. For datatransmission via the directional indicator line, the loads, i.e. thedirectional indicators, need not be in operation. Another advantageousembodiment transmits the data symmetrically over both directionalindicator lines that are present.

For use in a vehicle that has a tractor vehicle and a trailer, it isadvantageous if only a first control device is authorized to forwarddata. The further control devices that are connected interrupt theirdata transmission if they detect a further control device.

Advantageous monitoring of the second control device to determinewhether a first control device is connected is accomplished, forexample, by eavesdropping on the signals of the first device in the datastream. For this purpose, the second control devices are equipped with atime delay. In this delay time, they eavesdrop on data that the firstcontrol device is sending immediately.

It is furthermore possible to detect a first control device by measuringthe current of the electrical load.

All known transmission techniques can be used as the modulation andcoding method, but frequency shift keying is preferably used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary embodiment where the data passes via thesupply line of the control device.

FIG. 2 shows an exemplary embodiment which includes a trailer having asecond control device is also involved.

FIG. 3 shows an exemplary embodiment which includes data transmissionvia the directional indicator lines.

FIG. 4 shows an exemplary embodiment which includes a trailer operation.

FIG. 5 shows an exemplary embodiment which includes symmetrical datatransmission.

DETAILED DESCRIPTION

FIG. 1 shows a vehicle 20 that is equipped with a reversing aid. Controldevice 7 for the reversing aid is located at the rear of vehicle 20 andis connected to sensors (not illustrated) which sense the distance to anobstacle. Control device 7 is connected to electrical supply line 10 forreversing light 9 a. Located in line 10 is switch 4 which, when thevehicle is moving backward, establishes contact to power supply unit 22,generally the battery. Supply line 10 is also connected to display 8 forthe reversing aid. Further supply lines 11 and 14 are connected tobattery 22 via directional indicator relay 13, and provide power todirectional indicators 5 a and 5 a′.

When vehicle 20 is backing up, switch 4 for reversing light 9 a is alsoclosed. Control device 7 and display 8 are then supplied with voltagefrom battery 22. The signals going to the control device from thesensors (not depicted) are analyzed in the control device and must besent on to display 8. The data are forwarded serially via electricalsupply line 10 (a two-wire supply line) to display 8.

FIG. 2 schematically shows the circuit in a vehicle 20 and a trailer 21.The individual components have already been described in FIG. 1.Coupling of the tractor vehicle to trailer 21 is accomplished via plugconnections 3. In addition to control device 7 present in tractorvehicle 20, control device 6 of trailer 21 is located in thecontinuation of supply line 10. Electrical supply line 10 suppliesvoltage both to reversing light 9 a of tractor vehicle 20 and toreversing light 9 b of trailer 21. Installed inside display 8 is adetector 17 for a current measurement system. Located inside controldevice 7 are detectors 15 for a current measurement system or for amodulation measurement system 16.

When the vehicle is traveling backward, switch 4 for the reversinglights is closed. Both reversing lights 9 a and 9 b are thus inoperation. Both control devices—control device 7 in tractor vehicle 20and control device 6 in trailer 21—analyze data that are furnished fromexternal sensors (not illustrated). Initially, all the control deviceslocated in supply line 10 transmit their data to display 8. All the datathat are transmitted by the control devices via the supply line areimpressed onto the supply line by current modulation or voltagemodulation. All known techniques are possible as modulation methods andcoding methods, taking into account the transmission properties of thelines. A transmission method which meets applicable EMC specificationsmust, however, be used. A frequency shift keying (FSK) method isadvantageous, since it causes only minor electromagnetic interference inthe frequency range up to 10 kHz. It is particularly advantageous to usea pulsed FSK method, since transmission is thereby reliable while thecurrent load is minimal and the functional influence of the loads is notmeasurable. The frequency spectrum of active electromagneticinterference is also limited to a narrow band.

In FIG. 2, data from control devices 7 and 6 are being transmitted oversupply line 10. As soon as more than one control device is present in avehicle, the control devices must be prevented from transferring datasimultaneously to the display, thus causing confusion. Communicationbetween the control devices and the display is initially realized asone-way communication between a control device and a display. As soon asvehicle 20 has a trailer 21, actions must be taken to prevent bothcontrol devices from simultaneously transmitting data via supply line10. In the simplest case, this must be done by defining a ranking of thetwo control devices. In the simplest case, control device 7 is definedat the factory as the control device of a tractor vehicle, and controldevice 6 as the control device of a trailer. If only control device 7 inthe tractor vehicle is present, the control device begins to receivesignals from its sensors as soon as supply line 10 is closed via switch4. Since this is the control device of the tractor vehicle, it possessesan internal time delay circuit which prevents the received data frombeing immediately forwarded via line 10 to the display, and whichbuffers the data. Once the internal time delay has elapsed, the databuffered in control device 7 are transmitted to the display.

If a trailer 21 is coupled to trailer vehicle 20, control device 7initially knows nothing about the presence of control device 6. Controldevice 6 is designed so that it contains no time delay for thetransmission of data from the sensors to the display. As soon as thevehicle with trailer backs up and the switch for reversing lights 9 aand 9 b is closed, the control device begins to collect data from itssensor and transmit them via line 10 to the display. Control device 7has a time delay, and in the meantime collects data from its sensors.Simultaneously, control device 7 eavesdrops by way of a detector 16 onsignals that are impressed onto supply line 10. Since the control devicein trailer 21 immediately begins to transmit data, these data fromcontrol device 7 on line 10 are recognized. Control device 7 isimmediately muted, and transitions into a check function which simplymonitors data transmission on supply line 10. When trailer 21 isuncoupled, no further signals arrive from control device 6. If thevehicle then backs up, control device 7 once again collects data fromits sensors, buffers it during the delay time, and forwards it todisplay 8, since no data are detectable on supply line 10.

The assignment of a particular control device in one vehicle to aparticular position need not be made via hardware configuration.Solutions using pin coding of the control device terminals are alsoconceivable, so that the devices recognize by way of their connectionsthe position at which they are being used in the vehicle.

Detection of control device 6 can also be accomplished via a differentmethod. For this, a current measurement 15 is performed in controldevice 7. The measurement is accomplished on the common supply line 10for the control devices. The current measurement which detects theadditional power consumption of control device 6 can also be made via asensor 17 which can be located either in the display or at one of theloads, e.g. directional indicators 9 a and 9 b.

FIG. 3 shows the circuit in a tractor vehicle 20, for an alternativetransmission method. The individual components correspond to theconstituents already described in FIG. 1. Control device 7, which issupplied with voltage via electrical supply line 10, is supplied withvoltage when switch 4 is closed, i.e. when the vehicle is backing up.The signals from the sensors of the reversing control device aredelivered by control device 7 onto supply line 11 of right-handdirectional indicator 5 a′. Upstream from directional indicator relay13, signal converter 12 taps the signal from supply line 11 and forwardsthe signal to display 8. The data are forwarded via electrical supplyline 11 even when electrical loads 5 a and 5 a′ (the directionalindicators) are not in operation, since directional indicator relay 13is not located within the transmission section.

FIG. 4 depicts the circuit for the case of operation with a trailer. Thecomponents of the circuit have already been described in detail in FIG.2. In this exemplary embodiment, the data from control device 6, whichis located in trailer 21, are forwarded via supply line 14 ofdirectional indicator 5 b, while the data from control device 7 in thetractor vehicle are transmitted via supply line 11 of directionalindicator 5 a′. In this exemplary embodiment, it is not necessary forcontrol devices 6 and 7 to know about one another. The two controldevices can transmit data via the separate supply lines 11 and 14.Signal converter 12 detects the signals, and forwards to the displayonly the data from control device 6 that are arriving over supply line14.

Alternatively, the power consumption on line 10 is detected either bycontrol device 7 via sensor 15, or by display 8 via sensor 17, so thatcontrol device 7 can be muted when the power consumption of controldevice 6 is detected.

FIG. 5 shows an exemplary embodiment with symmetrical data transmission.The reference characters are once again used by analogy with FIG. 1. Thedata from the reversing sensors are received by control device 7 andtransmitted symmetrically via lines 11 and 14. Signal converter 12receives the data and forwards them to display 8.

The exemplary embodiments described so far describe simple one-waycommunication between a control device and a display. Also conceivableas a way to carry out the present invention is a double-waycommunication system, data being exchanged among all the components. Aprerequisite for double-way communication is the fact that therespective control devices must know their positions in the tractor ortrailer. Position definition can be accomplished by installing specifieddevices, or by installation at a coding plug. It is also possible tobegin an initialization phase, in which the control devices discern anobstacle arrangement from which they themselves recognize the positionsat which they are located. One simple possibility for double-waycommunication is for display unit 8 to activate the respective controldevice 7 or 6, and for the corresponding control device to begin sendingdata only after it has been polled by display 8. In this case, thedisplay would first poll the control device of trailer 21. If it ispresent, it begins in turn to transmit information. If it does notreply, shortly thereafter the display unit polls the control device ofthe tractor, which only now becomes active. A prerequisite for this typeof communication is that all the units must be able to send as well asreceive. The control devices can be identical; the difference betweenthem consists in suitable software. The control devices have learned,during the initialization phase, the position at which they are located,and thus also the code to which they must react when queried by thedisplay. Double-way communication offers the possibility of connecting adiagnostic device in order to perform rapid fault analysis.

What is claimed is:
 1. A method for transmitting data by a plurality of control devices in a vehicle which receive and analyze the data for a reversing aid, comprising the steps of: transmitting the data to be displayed from the control devices to a display unit in the vehicle via at least one display unit electrical supply line; supplying the control devices with power via at least one control device electrical supply line of an electrical load in the vehicle; and defining a ranking of the control devices for transmitting the data.
 2. The method according to claim 1, wherein the at least one display unit electrical supply line and the at least one control device electrical supply line are the same line.
 3. The method according to claim 1, wherein the at least one control device electrical supply line includes a first line of the electrical load and the at least one display unit electrical supply line includes a second line of a further electrical load, the first line being different from the second line.
 4. The method according to claim 1, wherein the at least one display unit electrical supply line includes a plurality of electrical supply lines corresponding to the plurality of control devices for separately transmitting the data of the plurality of control devices.
 5. The method according to claim 1, wherein the control devices include a first control device and a second control device, the first control device being situated at an end of a supply line, the first control device beginning a data transmission after an initialization, the second control device beginning a data transmission after a delay period if the second control device is not detected by the first control device.
 6. The method according to claim 5, wherein, after the delay period, the second control device detects the data on at least one supply line by way of a detection system, and is muted after detecting the data of the first control device.
 7. The method according to claim 5, wherein, within the delay period, the second control device detects an additional power consumption on a supply line, and is muted after detecting the additional power consumption by the first control device.
 8. The method according to claim 5, wherein voltage is supplied to the plurality of control devices only when the vehicle is moving in a reverse direction.
 9. The method according to claim 1, further comprising the step of modulating the data using a frequency shift keying technique. 